Dosimetric benefits of respiratory gating: a preliminary study

Abstract

In this study, we compared the amount of lung tissue irradiated when respiratory gating was imposed during expiration with the amount of lung tissue irradiated when gating was imposed during inspiration. Our hypothesis was that the amount of lung tissue spared increased as inspiration increased. Computed tomography (CT) image data sets were acquired for 10 patients diagnosed with primary bronchogenic carcinoma. Data sets were acquired during free breathing, during breath‐holds at 0% tidal volume and 100% tidal volume, and, when possible, at deep inspiration corresponding to approximately 60% vital capacity. Two treatment plans were developed on the basis of each of the gated data sets: one in which the treatment portals were those of the free‐breathing plan, and the other in which the treatment portals were based on the gated planning target volumes. Dose‐mass histograms of the lungs calculated at 0% tidal volume were compared to those calculated at deep inspiration and at 100% tidal volume. Data extracted from the dose‐mass histograms were used to determine the most dosimetrically beneficial point to gate, the reduction in the amount of irradiated lung tissue that resulted from gating, and any disease characteristics that might predict a greater need for gating. The data showed a reduction in the mass of normal tissue irradiated when treatment portals based on the gated planning target volume were used. More normal lung tissue was spared at deep inspiration than at the other two gating points for all patients, but normal lung tissue was spared at every point in the respiratory cycle. No significant differences in the amount of irradiated tissue by disease characteristic were identified. Respiratory gating of thoracic radiation treatments can often improve the quality of the treatment plan, but it may not be possible to determine which patients may benefit from gating prior to performing the actual treatment planning.PACS numbers 87.53 –j; 87.53.Tf

Quantitative Assessment of Irradiated Lung Volume and Lung Mass in Breast Cancer Patients Treated with Tangential Fields in Combination with Deep Inspiration Breath Hold (DIBH)

“…The mean M 20 value of DIBH shows a lower irradiated lung mass than in NB. The mean reduction was 17% which is supported by Butler et al [4], who calculated, in a cohort of ten patients, a reduction by 19%. V 20 was increased in DIBH by 29%, whereas the percentage of V 20 was reduced in DIBH by 22%.…”

“…To quantify the changing lung density within breathing patterns, Butler et al [4] recommended the calculation of a dose-mass histogram (DMH), which is likely to provide a better estimation of the actual number of lung cells damaged by radiation than lung volume. Since conventional planning systems do not normally offer DMHs, the mean density of the ipsilateral lung was calculated from CT voxels.…”

Implementation of Feedback-Guided Voluntary Breath-Hold Gating for Cone Beam CT-Based Stereotactic Body Radiotherapy

“…From a lung DVH perspective, FGBH gating gives the best results, while gating at end expiration gives the worst results. Gating is often done at end expiration (15,16), as this phase is considered to reveal the most stable tumor location. This study indicates that this perceived increase in reproducibility needs to be balanced relative to the increase in relative lung volume.…”

Quality assurance evaluation of delivery of respiratory‐gated treatments

“…Despite evidence that more normal lung tissue is spared at deep inspiration, (7) our clinical practice is to gate at end expiration using amplitude-based gating. We have found end-expiration gating to be more reproducible and a more comfortable breathing position for the patient.…”

“…We have found end-expiration gating to be more reproducible and a more comfortable breathing position for the patient. (7) Treatment planning was done using computed tomography (CT) image data sets acquired by triggering a helical CT scanner (PQ-5000, Philips Medical Systems, Cleveland, OH) operating in axial mode to acquire single axial scans at end expiration.…”